Overruuning pulley:
[1] A vehicle travelling with no throttle and the engine acting as a brake is said to be "on the overrun" or "overrunning. "
[2] The action of a trailer when it travels faster than the towing vehicle.

Overrunning clutch:
[1] A clutch mechanism that will drive in one direction only. If driving torque is removed or reversed, the clutch slips.
[2] A part of a starter motor designed to avoid armature damage caused by severe overrunning.
[3] A device in an automatic transmission that disengages the engine on overrun.
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